Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
More specifically, some wind turbines, such as wind-driven doubly-fed induction generator (DFIG) systems or full power conversion systems, include a power converter, e.g. with an AC-DC-AC topology. Standard power converters typically include a bridge circuit, a power filter and optionally a crowbar circuit. In addition, the bridge circuit typically includes a plurality of cells, for example, one or more power switching elements and/or one or more diodes.
Such wind turbines can experience costly down time whenever a power converter, or other electrical devices, experiences a trip fault. Investigating the cause of the various trips can be time consuming and may require offsite or onsite root cause analysis. In addition, nuisance trips can cripple the availability of a wind turbine. The hardest or most difficult trips, which are the intermittent trips that usually cannot be troubleshot through traditional means because such trips cannot be repeated, generally abruptly and forcibly shut down the wind turbine and almost always require an operator to reset the fault. In other words, intermittent trips may be embedded in a circuit card, where repair and/or replacement can be difficult (if not impossible), time-consuming, and costly. In contrast, soft trips generally refer to trips that gently shut down the operation of the wind turbine and often reset automatically.
An example circuit diagram 10 of one embodiment of a simplified wind turbine power system is illustrated in FIG. 1. As shown, the illustrated circuit diagram 10 includes a power supply 12 (sometimes located uptower) with a circuit 14 that goes downtower to monitor one or more first electrical devices 16. In addition, as shown, the circuit 14 goes back uptower to monitor one or more second electrical devices 18, across a first slip ring 22 to monitor one or more third electrical devices 20, e.g. located in the wind turbine hub. Moreover, the circuit 14 travels back across a second slip ring 24 to a relay coil 26 associated with the second electrical device 18. As such, when the relay coil 26 loses power, the relay coil 26 electrically disconnects the circuit 14 and can only be reset when all of the electrical devices 16, 18, 20 are closed and a reset 28 is actuated.
In this illustrated circuit diagram 10, only three devices are illustrated. Wind turbine power systems generally include more than three devices, e.g. a dozen or more devices. Further, each of the devices is typically associated with nuances that make troubleshooting difficult. Even if troubleshooting could be completed, many of the devices are very expensive to replace. The relay coil 26 of the circuit diagram 10 is usually hypersensitive. In most cases, the relay coil 26 responds quickly (e.g. within four (4) milliseconds (ms)) and disconnects when the voltage is less than 80%. As such, conventional circuit diagrams of wind turbine power systems provide minimal ride-thru capability if needed.
The conventional circuit diagram 10 of FIG. 1 is further explained in the timing diagrams of FIGS. 2 and 3. As shown in FIG. 2, when a trip event occurs at time T1, the relay coil 26 disconnects. As shown in FIG. 2, the first and second electrical device(s) 16, 18 are capable of riding through the trip event because the event is very brief. In contrast, as shown, the third electrical device 20 drops out for a brief time period (e.g. about 3 ms) in response to the brief trip event. FIG. 3, however, illustrates a trip event of a longer duration. Thus, as shown, the first electrical device(s) 16 is capable of riding through the trip event, but still causes the entire circuit 14 to drop out. Moreover, as shown, the third electrical device(s) 20 drops out for a brief time period (e.g. about 10 ms), whereas the second electrical device(s) 18 fails to ride through the trip event because the relay coil 26 is too sensitive.
Thus, a system and method that addresses the aforementioned issues would be advantageous. Accordingly, the present disclosure is directed to a system and method for reducing hard trips in a wind turbine power system that also includes ride-through capabilities.